Truffle Node replacement problem caused by recursion

[Stefan Marr]

Hi Wei:

On 19 Oct 2013, at 01:44, Wei Zhang <ndrzmansn at gmail.com> wrote:

> Hi guys,
> 
> I came across a problem with Truffle node replacement when I was
> trying to apply Python level inlining to binarytrees.py (one of the
> shootout benchmarks). I thought it is worth sharing it with all of you
> that are using Truffle.
> 
> Basically, recursion might cause inconsistencies in a Truffle AST.
> That is a node's parent's children don't include itself.

I had similar issues. A simple fibonacci function is a good example.
The plus operation got specialized in a recursive call, and the unspecialized plus node was still on the Java call stack and tried to specialize itself after completing execution of its arguments.

My solution first was based on remembering in the node that it got specialized.
See [1] and [2] for the code in my nodes.

However, after I switched to using the Truffle DSL, that problem went away. Don't know exactly why.

And even more mysterious is a commit that was done by Andreas recently and later reverted: [3] "Truffle: fix node rewrite issue that can occur when a currently executing node is replaced in a recursive call."
Not sure why it got reverted later on, but since I am not experiencing the issue anymore, I hope it is solved somehow by the Truffle DSL implementation.

Best regards
Stefan

[1] https://github.com/smarr/TruffleSOM/blob/bf97e05836c0c9c9647b41e6da305c007ac94236/src/som/interpreter/nodes/MessageNode.java#L141
[2] https://github.com/smarr/TruffleSOM/blob/bf97e05836c0c9c9647b41e6da305c007ac94236/src/som/interpreter/nodes/MessageNode.java#L257

[3] http://hg.openjdk.java.net/graal/graal/rev/be0a33a631fa

-- 
Stefan Marr
Software Languages Lab
Vrije Universiteit Brussel
Pleinlaan 2 / B-1050 Brussels / Belgium
http://soft.vub.ac.be/~smarr
Phone: +32 2 629 2974
Fax:   +32 2 629 3525